This invention relates to all-optical logic elements, and more particularly to the use of interferometers with semiconductor optical amplifiers (SOA) and multi-mode interference (MMI) devices.
Since photons travel faster than electrons, much effort has gone into trying to develop an optical computer or optical logic elements. Different approaches have been taken to developing optical logic and other elements of a computer. Most of these approaches have proven to be difficult to produce, expensive, or bulky.
Optical logic gates are using an interferometer are disclosed by Roberts et al. in U.S. Pat. No. 5,999,283. FIG. 1A is a prior-art interferometer-based exclusive-OR (XOR) gate. A continuous-wave light input is split into two branches to semiconductor optical amplifiers (SOA) 6, 8. Modulated input A is combined with the output of SOA 8, while modulated input B is combined with the output of SOA 6. Outputs of SOA 6, 8 are combined to produce the logic-gate output C.
The logical input signal A combines with the output of SOA 8, either constructively or destructively, depending on the phase difference. Likewise, constructive or destructive interference occurs where input B is combined with the output of SOA 6. Finally, constructive or destructive interference occurs where the two interferometer arms are combined to generate the final output C.
SOA 6, 8 have the same phase shift when A and B are at logic 0. The output C is a logical XNOR of A and B. SOA differ in phase shift when A and B are at logic 0 by xcfx80, and output C is the logical XOR of A and B. FIG. 1B shows the XOR function when the SOA""s have a zero phase difference. FIG. 1C shows that the interferometer gate is an XNOR gate with a third continuous-wave input.
While useful, the counter-propagation of the logical inputs can feed back to the continuous-wave input, which may cause cross-talk among other gates that share the same continuous-wave signal source. Splitting of the continuous-wave signal power may not be the ideal 50%-50% due to geometry or orientation imperfections of the Y-junctions.
The parent application disclosed optical logic gates using semiconductor optical amplifiers (SOAs) configured in a cross-gain modulation (XGM) mode. The parent application uses and multi-mode interference (MMI) splitters/combiners to better control optical power. The inventors realize that phase modulation may be used in place of gain modulation for the optical logic gates.
Optical logic gates are desired that employ phase modulation and interferometric techniques with multi-mode interference (MMI) devices for better optical power distribution and control.